1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus in which ultrasonic pulse beams are transmitted into an organism, ultrasonic waves reflected within the organism are received to obtain received signals, and an image is displayed in accordance with the received signals thus obtained.
2. Description of the Related Art
Hitherto, there has been widely used for the purpose of diagnoses of a disease inside an organism, particularly, the human body an ultrasonic diagnostic apparatus in which ultrasonic waves are transmitted into the organism, and the ultrasonic waves reflected at tissues within the organism are received to obtain received signals, so that an image is produced in accordance with the received signals thus obtained.
As one of functions incorporated into such an ultrasonic diagnostic apparatus, there is known a so-called color-Doppler mode in which there is utilized such a Doppler phenomenon that when an ultrasonic wave is reflected on a blood flow within the subject, the reflected ultrasonic wave undergoes a frequency transition according to a direction of the blood flow and a velocity of the blood flow, components, which undergo a frequency transition, of the reflected ultrasonic wave are extracted to detect a direction and a velocity of the blood flow on the respective point, and a tomographic image (a color-Doppler image) wherein for example, a blood flow involved in a direction coming to an ultrasonic probe serving for transmission and reception of ultrasonic waves, a blood flow involved in a direction going away from the ultrasonic probe, and a velocity of a blood flow are represented by red, blue and luminance, respectively, is displayed.
Further, there is also known a so-called power-Doppler mode. As mentioned above, according to the color-Doppler mode, components, which undergo a frequency transition, of the reflected ultrasonic wave are extracted to detect a direction and a velocity of the blood flow on the respective point. On the other hand, according to the power-Doppler mode, components, which undergo a frequency transition, of the reflected ultrasonic wave are extracted to detect a power of the component undergoing the frequency transition on each of points within the tomographic plane, and a tomographic image (a power-Doppler image) wherein the magnitude of the power is represented by luminance or colors, is displayed. The power-Doppler image has, as compared with the color-Doppler image, an aspect that while it is unclear as to velocity and directions of a blood flow, it is displayed with more favorable S/N as to existence of a blood flow.
Hitherto, in the color-Doppler mode, it is used in such a manner that for example, two color-Doppler images are put side by side, and as one of those two images an image at a certain time point (a certain one frame of image) is displayed on a stationary basis (it is referred to as a "freezing" that a certain one frame of image is continued to display, and the image displayed in this manner is referred to as a "freeze image"), and as another of those two images an image representative of a blood flow distribution is displayed on a real time basis. The color-Doppler mode is mainly used for a diagnosis of a heart.
In view of the fact that recently performances of the color-Doppler mode and the power-Doppler mode are improved, those modes are becoming used also for a diagnosis of the abdominal region which abounds in faint blood flows as compared with the heart. An important matter of concern in a diagnosis of the abdomen is the presence of a tumor in the abdomen and the presence of blood flows flowing inside the tumor. As mentioned above, as to drawing the presence of a blood flow per se, the power-Doppler mode is more excellent as compared with the color-Doppler mode, and is becoming noticed. However, when it is required to make a closer diagnosis, it is also important to grasp the behavior of the blood flows flowing inside the tumor, that is, a blood direction, a blood velocity and their variations in time. The power-Doppler image involves no information as to those messages. Thus, in order to obtain information as to those messages, it is obliged to utilize the color-Doppler image even if it is poor in S/N ratio.
For example, even if it is intended that the power-Doppler mode is selected beforehand to identify on the power-Doppler image the presence of the blood flow inside the tumor, and then the mode is switched to the color-Doppler mode to identify on the color-Doppler image directions and velocity of the blood flow inside the tumor, it happens that even if the presence of the blood flow inside the tumor can be identified on the power-Doppler image, it is difficult after changeover to the color-Doppler mode to identify the associated blood flow on the color-Doppler image, since the blood flow of interest is originally an extremely fine blood flow, and a quantity of blood flowing therethrough is small, and in addition the color-Doppler image involves a poor S/N ratio.